Is there a baseball/soccer/sports field close by with flood lights? and were they switched on? There are 2 parks close by which come to mind and there are underground cables that supply electricity both to a nearby facility and also the floodlights for the baseball field, which send my Safari into the chatter symphony. Not even lowering the sensitivity all the way down will completely eliminate the chatter. I think you'll find that there are either overhead power lines or underground cables/lines and vaults somewhere there which are triggering the chatter your experiencing.
P.s. I've yet to find a location that the ground itself was the cause of it being undetectable and that didn't have power lines either under or over the park or close by.

I had a bad dose of 'cabin fever' again!!lol yesterday and so I ventured out in the heat (mid to high 90's) and went to a park which I think Happa54 was referring to, De Anza park? in Ontario. There are power lines along one nearby street and floodlights for the baseball field and underground cables and a box or 2 above ground. I experienced lots of EMI like he did and it did send my Safari into uncontrollable chattering. All I could do is wander around and pick spots where there wasn't any or little EMI and detect. I tried lowering the sens and it worked in a few places but because of the heat, got too tired and left after about 1 1/2 hrs. I did manage to get a few quarters and what's in the pic but no gold or silver. The park is big enough to have spots where you can definitely detect AND it's an old park like Happa54 mentioned so I'll be back and cover the park more thoroughly!

P.s. When I got to the park, there was already a detectorist there. He had recovered a few coins and a little later I saw from a distance that he quit after I had chatted with him. I found his headphones (Garrett's) in a trash can with the wires pulled out of them. I felt sorry for him that his headphones failed him or he accidently snagged them? and that reminded me to always carry a spare set of headphones because something like that can really ruin your day. Always carry back-up equipment! Stay hydrated my friends! lol

Yesterday, I went back to this same park even though it was hot as hades!! and confirmed again how much EMI was all around this park. There are just a few spots where you stand any kind of chance to get a few coins. Even walking so far away from any power lines and floodlights for the baseball field, the interference is incredible! Lowering the sens all the way down and ground balancing multiple times didn't help at all. While there is a chance to detect some good targets, I'll have to pass on this park and look for fresh places to detect!!!

There are a couple of parks in the San Gabriel Valley with huge Edison power lines overhead and huge ball field lights, etc where I occasionally hunt and I don't have to make adjustments to my normal sens settings. Noise cancelling is always something I do every 20-30 minutes.

But this park it really too much. There must be something else that is working in conjunction with all of this that has created this area to be unhuntable.